Feedthrus are used to connect conductive elements of two or more electrical devices. By way of example, where a first electrical device is located in a particular environment, such as, for example, a vacuum environment, a high or low temperature environment, or a particular gas environment, including, an explosive gas environment or a low or high moisture environment, and one or more other electrical device are located outside the particular environment of the first electrical environment. In such an example, one or more feedthrus may be provided that connect the two or more electrical devices in a manner that permits isolation of the particular environment of the first electrical device.
To permit connection of the one or more electrical devices, the feedthru is provided with at least one conductive pin that extends through a header, which functions as a barrier between two sides of the conductive pin. Where the header is a conductive material, an insulating material may be located around the portion of the conductive pin that extends through the header in order to prevent an electrical current passing to the header or between the pins. Where the header is a non-conductive material, the header itself may function as an insulating material that prevents an electrical current from passing between the pins. In this manner, the first side of the conductive pin may connect to a conductive element, such as, for example, a wire or terminal, connected with a first electrical device and the second side connects to a conductive element connected with a second electrical device to provide an electrically conducting pathway between the first and second electrical devices.
Since at least a portion of the first and second sides of the conductive pin must be exposed in order to connect the conductive pins to the conductive elements, where the header is a conductive material, where the feedthru includes more than one pin, or where the feedthru contacts some other conductive material, creepage breakdown can cause short circuiting. At high temperatures, creepage breakdown is even more problematic, since moisture tends to condense more readily at elevated temperatures. For example, where the feedthru includes a plurality of pins, a layer of moisture may condense on any insulating material and provide a conductive pathway between the pins. By way of yet another example, where the header is a conductive material, a layer of moisture may condense the insulation material and provide a conductive pathway between one or more pins and the header.
It has been observed that contamination on the surface of any insulating material located around the conductive pins of the feedthru may exacerbate this problem. By way of example, such contamination may provide a point for the moisture to condense. By way of yet another example, such contamination may dissolve into any condensate to form an electrolyte that itself generates voltages over 100 mV.
One approach to solving this problem involves providing a coating of an insulating material on the exposed portions of the pins and/or in situations where the header is a conductive material, on the header. In this manner, the creepage distance can be increased. Furthermore, an insulating material can be used to coat any exposed conductive material, i.e. the exposed portions of the pins, the exposed portions of the conductive elements, and, if used, any brazed or soldered material used to connect the pins to the conductive elements. Assuming the insulating material is impermeable to moisture, in this manner creepage can be eliminated if all exposed conductive materials are coated. One type of insulating material used for this purpose is Lektro-Tech, an electrical and mechanical corrosion preventive compound including 3,3-dichloro-1,1,12,2-pentafluoropropane, 1,3-dichloro-1,1,2,3-pentafluorpropropanecyclohexane, oxygenated hydrocarbon, and carbon dioxide propellant. This compound is effective at forming a barrier over exposed conductive material to increase creepage distances or to significantly eliminate creepage breakdown.
Although Lektro-Tech is effective at preventing short circuits in temperatures ranging from about 150° C. to about 205° C., use of Lektro-Tech has been ineffective at preventing short circuits where the temperature of the operating environment exceeds about 205° C. However, as previously mentioned, unless adequate ventilation is provided condensation is more likely to occur as the temperature increases.
The present invention relates to a feedthru including a ceramic based coating and a method of applying a ceramic based coating to a feedthru.